Flotation of culm



" disposing of the slush culm which is usually Patented 8,

'PATENTOFFICE' FLOTATIONOF CULM Norman Hadley, Westfield, N. J., aaim'rto "American Cyanamid Company, N. Y., a corporation of Maine,

N ew York,

a. Drawing. Application- September 1, 1936, v 1 Serial No. 98,975 4Claims. (or. 209-166) This invention relates to the flotation of. slushculm and other refuse coal. In .a more specific modification, theinvention is especially concerned withthe recovery of 'low ash coal fromanthracite:

- slush culm or other anthracite refuse.

"The problem of coal refuse, both bituminous and anthracite, has longbeen a serious one in the industry. The refuse coal is mainlycontaminated with high ash material and is not useable as such. As aesult, serious losses of good coal: in flnesizes ares'ufiered by theindustry, and they have to incur considerable expense in pumped intolarge culm banks. Many-mines do not have sufli'cient fairly level groundfor culm banks. and when the banks are placed on too great a slope, rainwashes thecoal into the rivers and a seriousnuisance. frequently arises.Slush culm banks, particularly bituminous coal, also tendto ignite andburn for years with serious annoyance from smoke and fumes. representedby the good coal in the culm or'other refuse are, of course, much moreserious'in the anthracite industry than in the bituminous inin thebreaker and I dustry, because the unit value of anthracite coal ishigher than bituminous and the character of the anthracite coal resultsin greater degradation hence larger proportions of the slush culm.

Flotation of .coal refuse has been proposed and has been used fairlyextensively in Europe prithat bituminous coal represents asomewhateasier flotation problem.

When refuse coal is floated. such as anthracite slush culm, and in thefollowing more specific discussion of the invention the descriptionwill/be based on the purification of anthracite slush culm although itshould be understood that the features are also applicable to.bituminous coal, the

culm contains a mixture of materials varying both in size and incomposition. That is to say, there is a certain amount of coal, forexample about 60% in representative anthracite culms, which is very lowin ash, containing less than 10% of ash and approaching the actualinherent coal ash for coalfrom that particular area. This good coaloccurs in a wide range of sizes running from down to very fine particlesless than 100 mesh (Tyler Standard Series). The accompany+ ing 40% ofhigher ash material, of course, grades c contaminated by anyconsiderable portions of frommaterial with only slightly higher ash thanalso occurs in practically The losses lern even more difficult.

the good coal, down to material which is mostly ash with only littlecoal.

as the good coal. v

The flotation ofcoal, using standard flotation reagents which are forthe most'part hydrocarbons such as kerosene accompanied, if necessary,by suitable frothers, is based on wettability of the coal by the oil andthe'coal therefore tends to attach itselfto the froth bubbles andappears in the concentrate. Since, however, the material coal (havingonly inherent ash) to a slaty gangue impregnated with small amounts ofcoal, it is diflicult and has hitherto been impossible to oh- This highash material as wide a range of sizepresent in the culm grades all theway from pure tain a sharp flotation separation with good re-' coverysuch as is commonly found in the flotation of 'sulflde minerals and freegold because the good coal is not'entlrely liberated from the gangue.The problem might be considered as one in which it was necessary tofloat a concentrate of mineral values away from a partlymineralized Jgangue. Due to the fact that the coal to be recovered forms a largepropcrtion of the feed.

usually somewhat over half, avery large bulk of onthe flotation machinesand renders the. prob- The goal of a flotation cleaned coal fromanthracite culm is less than 10% ash. It has been proposed to,fioatslush culm by grinding down to a uniform fine size. These proposalsare without economic value as the grinding plant is as large as theflotation plant and the result of grinding reduces the value of theclean coal obtained.

Previous attempts to clean anthraciteslush culm followed the generalflotation procedure which has been used withslight success on bituminousconcentrate which contains a large portion of the good coal, say from80% up, but such a concentrate is not low in ash and cannot beeconomically cleaned. Attempts to improve the grade of thecoalooncentrateby reducing the amount of reagents used'were alsounsuccessful. It was possible toobtain a concentrate of the des red ashcontent but only at the expense of very serious losses in recovery. Allattempts to vary flotation procedure failed to produce both goodrecovery and a lowash concentrate.

.The presentinvention is based on the discovery' that it is possible tofloata full size range of refuse coalsuch as anthracite slush culm, witha very'small. amount of-reagents so that classified preferably byscreening and the fine iii material which consists almost exclusively offine high ash material, is rejected. The coarser material, while itcontains all of the coarse low ash coal, is still contaminated with acertain amount of coarse high ash material, and therefore screening of\the tailings will not recover the coarse coal in the form of asufliciently low ash material. However, the oversize from theclassification of the tailings can then be floated under conditionswhich will result in the flotation of coarse low ash coal particles anddiniculties will not be encountered because the high ash material is alllikewise coarse and therefore does not float oil into the concentrateand the problem of contamination with high ash material is solved.

The present invention not only results in obtaining 25. better recoveryof low ash material, but also results in an increased capacity offlotation equipment. The consumption of collector which is usuallykerosene or a similar .hydrocarbon, is aiso ,decreased. I

It is an advantage of the present invention that the standard reagentscan be used. However, it has been found that a frother consisting ofparaflin alcohols of 7 to carbon atoms stabilized with a hydrocarbongives better results and in a more specific aspect the inventionincludes this feature.

While the invention may be used with any type I of flotation machine,best results are obtained with mechanical machines.

are well suited for floating the. wide range of sizes -which isnecessary in carrying out the present invention.

The process of the invention is very flexible and is well adapted tohandle refuse coal of difl'erent types to produce products for variousmarkets. Thus, forexample, in many cases there is a good market at ahigher price for coarser coal sizes and it is desirable to keep the finerougher concentrate separate from the floated coarse portion of thetailings. In other cases, for example where the clean coal .is to bepulverized, it may be desirable to mix the two final products together.

Where the ash requirements are not unduly severe, therougher concentratemay remain uncleaned-but where the minimum ash is required, it isdesirable ,to clean the rougher concentrate as such aycleaning operationwill greatly reduce the ash without material loss in good coal. Ofcoarse, the additional cleaning operation of the rougher concentratenecessitates additional flotation equipment .and slightly increases theamount of reagents. The particular compromise best suited for any givencondition is largely determined by economic considerations and it is anadvantage of the present invention that it is flexible and that the bestand most profltabl compromise can be chosen.

The invention will be described in greater ae-v areas-i1 tail inconjunction with the cleaning of anthracite slush culm from the bank orlcurrent production of the Philadelphia 8; Reading Coal it Iron, Company.it should be understood that the exact details of flotation type,reagent consumption, and the like, will vary somewhat with difierentculm and with different coals, and the invention is therefore in nosense limited to the precise details of the specific examples.

Example 1 Slush culm from the Locust-Summit Breaker of the Philadelphiain Reading Coal a Iron Company was floated in standard Fagergrenflotation machines with .276 lb. per ton of a frother consisting of amixture of paraffin alcohols or" 7 to 10 carbon atoms and stabilizedWith a hydrocarbon, and which is described in the patent of Christmannand Jayne No. 2,065,053 issued December 22, 1936, without anyhydrocarbon collector. A concentrate was obtained which contained finecoal only, then the tails were classifled in the presence of 0.5 lb. pertonof sodium silicate and after rejection of the finer material5 lbs.per ton of kerosene were added to the residual pump at about 50% solidsand the pulp then diluted to solids and floated in a second set offlotation machines.

The original culm had an ash content of -26%, and the results obtainedby the treatment are summarized in the following table:

Cumulative Weight, Ash,

Product percent percent Weight Ash,

percent percent Gone 1 23.55 121 26.56 12.1 Gone. 44. 14 11.0 70. 70 11.4 Tail 1e. 55 56. 0 s7. 25 1o. 9 Rejected fines Ta 75 622 100.00 25.3

Example 2 High ash 51am culm from the Locust-Summit Breaker of thePhiladelphia & Reading Coal 8:

Iron Company having approximately 40% ash, was floated at 21% solids instandard Fagergren flotation machines with .0322 lb. per ton of thefrother described in Example 1. A rougher concentrate is obtained whichcontains the fine low ash coal. The remaining pulp is then screened at28 meshand .092 lb. per ton of frother and 4 lbs. per ton of keroseneadded to the"+28 mesh material. This coarse material is floated to givea second rougher concentrate, and both rougher concentrates are cleanedusing .092 lb. per ton of additional frother in each case. The resultsobtained are shown in the following table:

In'the claims the term coal of frotmflotation size" is intended to covercoal of a size passing through 10 mesh screens and'has no-other mean-- ling. This represents about the coarsest coai which can be floated by afroth flotation process.

What I claim is:

1. A method of cleaning refuse coal which comprises subjecting therefusecoal of froth flotation size to'a froth flotation process with an 1amount of reagent insufllcient to float flne high ash particles wherebya concentrate is produced containing a major portion of flne low. ashcoal particles, classifying the flotation tailings, rejecting the finesizes and subjecting the coarse particles. I r

2. A method of cleaning anthracite slush culm culm of mm flotation sizeto a froth flotation process with anamount of reagent insufllcient tofloat fine high ash particles whereby a con v cen'trate is producedcontaining a major portion oi flne low-ash coal particles, classifyingthe flotation tailings, rejecting the fine sizes and subjecting thecoarse sizes to froth flotation with an s. A method according to claim 2in which'the tailing is sized on a screen at approximately 28 whichcomprises the anthracite noam nsnmr,

' amount of-fiotation reagent suflicient to float coarse low ashparticles.

